JPS61235782A - Emission ct device - Google Patents

Abstract

PURPOSE:To obtain a tomographic image which is quantitative by fitting a surface ray source having a nuclide different from RI (radioisotope) in a body to be detected to the 1st detector, calculating the coefficient of absorption of gamma rays on the basis of the gamma rays from the surface ray source which are detected by the 1st and the 2nd detectors, and correcting the absorption of the tomographic image of the object body by using the coefficient of absorption. CONSTITUTION:The surface ray source 10 having a nuclide different from the RI in the object body is fitted to the 1st detector 5. The gamma rays radiated by this surface source 10 are incident on the detector 5 through a parallel hole collimator 9 and also incident on the 2nd detector 6 through a parallel hole collimator 11, the object body P, and a collimator 12. The outputs of the detectors 5 and 6 are inputted to a data collection part 14, whose output is inputted to an arithmetic processing part 16 through a memory 15. This processing part 16 calculates the coefficient of absorption of the gamma rays by the object body P on the basis of the gamma rays radiated by the surface source 10 and corrects the tomographic image of the object body P by using the coefficient of absorption, so that the reconstitution result is displayed 18 through a memory 17.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention collects emitted γ-rays by rotating a detector around a subject to whom a radioisotope (hereinafter referred to as rRIJ) has been administered. The present invention relates to an emission CT device that obtains tomographic images of the distribution in the body.

[Technical background of the invention and its problems] Conventional emission CT devices use, for example, an Anger-type gamma camera as a radiation detector, and move this detector around the subject stepwise or continuously. This detector detects and collects gamma rays emitted from the object in all directions on the quadrature plane of the detector, and processes all the obtained detection data to detect the 3D image inside the object. I am getting a good image.

FIG. 4 is an explanatory diagram of the principle of obtaining projection data in an emission CT apparatus.

Collection of gamma rays to obtain a three-dimensional image is carried out by the detector 3.
By arranging the parallel hole collimator 3 between the object P and the subject P, only the gamma rays incident perpendicularly to the detection surface are selectively detected. The projection image P (X, θ
) is expressed by the following formula.

P(X.θ) = fA(x, y)e ”' Y)d
Y... (1) In formula (1), separate the term foe `` '' Y) d Y , (2) and write P (X, θ) '' F f A (x, y) d Y =
In order to obtain C.[3], μ(x, y) is assumed to be constant, and a correction table C(x, y) is determined for the entire reconstructed image.

C(X, V) is expressed as shown below.

C(X, V)-1/ (1/ (2π) f, exp(-μm12θ) dθ)
(4) Then, using this C(x, y), an ECT image (tomographic image) is obtained which is absorption-corrected according to the following equation.

f (x, V”) −f o (x, V) ・C(
x, V) = (5) fo: tomographic image before absorption correction f: tomographic image after absorption correction However, even if absorption correction is performed using equation (5),
Since the distribution of the absorption coefficient within the subject P is not constant,
There is a problem in that appropriate absorption correction cannot be performed, and therefore quantitative ECI images cannot be obtained.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to provide an emitter CT device that can obtain quantitative ECT images by performing appropriate absorption correction. It is.

[Summary of the Invention] The outline of the present invention for achieving the above object is to rotate around the subject while facing each other through the subject, and emit radiation from a radioactive isotope administered to the subject. The first one that can detect gamma rays. a second detector; In an emission CT device that obtains a tomographic image of a subject based on gamma ray information collected by a second detector, the first detector is made of a nuclide different from a radioisotope in the subject, and a surface radiation source attached to the first ray source;
Absorption coefficient calculation means for calculating the absorption coefficient of γ-rays based on the γ-rays from the surface ray source detected by the second detector, and using the absorption coefficient calculated by the absorption coefficient calculation means. and absorption correction means for performing absorption correction of the tomographic image of the subject.

[Embodiment 1 of the invention Hereinafter, the present invention will be specifically explained with reference to Examples.

FIG. 1 is a block diagram of an emission CT apparatus which is an embodiment of the present invention. 5 is a first detector, and 6 is a second detector. This first. The second detectors 5 and 6 rotate around the subject P in the direction of the arrow 7 while facing each other through the subject P, and the second detectors 5 and 6 rotate around the subject P in the direction of the arrow 7, and the γ rays γi emitted from the R1 administered to the subject P. , γj, etc., and is rotatably supported by the gantry 8.

In front of the first detector 5, a first parallel hole collimator 91 and a plane radiation source 10. A second parallel hole collimator 11 is attached. The surface radiation source 10 is formed into a thin plate shape using a different nuclide from R1 to be administered to the subject.

The γ-rays emitted from this surface ray source 10 enter the first detector 5 via the first parallel hole collimator 9, and also enter the first detector 5 through the first parallel hole collimator 9.
Parallel hole collimator 11. The light is made to enter the second detector 6 via the subject P and the third -'' remeter 12.

14 is the first. The output of the second detector 5.6, i.e.
This is a data collection unit that takes in the X, Y amplifier blanks and Z signals (signals proportional to the energy of γ-rays), and the A/D (
It consists of an analog/digital) converter and a pulse height analyzer. The pulse height analyzer captures only the photoelectric peak of a predetermined nuclide and outputs an output for each different nuclide. The output of this data collection unit 14 is stored in a memory 15 arranged at a subsequent stage.
It is designed to be written for each different nuclide.

Reference numeral 16 denotes an arithmetic processing unit that performs calculations such as data filter processing, back projection processing, correction processing, etc. based on the stored contents of the memory 15, and for example, a CPLI (central processing unit) is applied (described in detail later). ). The output of this arithmetic processing section 16 is provided to display a tomographic image on a display section 18 via a memory 17 arranged at a subsequent stage.

Next, details of the arithmetic processing section 16 will be explained based on FIG. 2.

FIG. 2 is a block diagram showing details of the arithmetic processing section in the device of this embodiment. As shown in the figure, this arithmetic processing section 1
Functionally, filter processing means 19 performs filter processing of information using γ rays emitted from the plane line [10], and filter processing means 19 performs filter processing of information using γ rays emitted from the RI within the subject P. A filter processing means 20, an absorption coefficient calculation means 21 that calculates the absorption coefficient of the gamma ray in the subject P based on the output of the filter processing means 19, and a back projection process based on the output of the filter processing means 20. The present invention includes a back projection processing means 22 for reconstructing a tomographic image X(i, j) of the subject P, and an absorption correction means 23 for performing absorption correction on the reconstructed image from the back projection processing means 22. It is composed of

Here, the absorption coefficient μ in the absorption coefficient calculation means 21 is
The calculation of is expressed by the following formula.

μ=-j! n (1/Io)
(6) In equation (6), Io is the intensity of γ-rays emitted from the surface ray source 10 and before passing through the object P, as shown in FIG. γ after passing through P
It is line strength. 1st. Second parallel hole] Remeter 9゜11
If the sensitivity ratio of
The gamma ray intensity detected by 1 can be replaced with 10. Therefore, the equation (6) can be transformed as shown in the following equation.

μ−1n<Δ·I/11) (8) The absorption correction means 23 calculates an absorption coefficient distribution image M as shown in FIG. 3 based on the absorption coefficient from the absorption coefficient calculation means 21. Create (X, V). M(x, y) is expressed as in the following equation.

M (X, V>-1/ (1/ (2π) feXp(-μ(X, V)・Jl
o) dθ)...(9) Then, from the created distribution image M(x, y), the absorption coefficient t'
Create an Xl matrix M(i,j), and this M(i,j
), the absorption correction of the reconstructed image from the back projection processing means 22 is performed. The absorption correction is expressed by the following equation.

X' (i, j)=X(i, j)・M(i, j)
... (g) X' (t, j): Reconstructed image after absorption correction In the above configuration, the first. Second detector 5, 6
The X, Y amplifier blanks and 2 signals detected by
The data is captured by the data collection unit 14, converted into a digital signal, and then written into the memory 15 for each different nuclide. Information on the γ-rays emitted from the surface ray source 10 is input to the absorption coefficient calculation means 21 via the filter processing means 19, and the absorption coefficient μ of the γ-rays in the subject P is calculated by executing the calculation of the above equation (8). Provided for calculation.

On the other hand, information on the γ rays emitted from R1 in the subject P is transmitted to the back projection processing means 22 via the filter processing means 20.
and reconstructed image X(i, j) by back projection processing.
used for the creation of

Based on the absorption coefficient calculated by the absorption coefficient calculation means 21, the absorption correction means 23 creates an absorption coefficient distribution 111+M(x, y) by executing the calculation of the previous equation (9), and the created distribution image M(x , y), the absorption coefficient matrix M(i
, j), and performs absorption correction on the reconstructed image by executing the calculation of the previous equation. Reconstructed image X' (i
, j) are displayed on the display unit 18 via the memory 17.

In this way, in the device of this embodiment, R1 in the subject P
A surface radiation source 10 of a different nuclide is attached to the front surface of the first detector 5, and R1 emitted from the surface radiation source 10 is detected by the first detector 5, and is also detected by the second detector 5 through the subject P. Since the absorption coefficient of gamma rays by the subject P is calculated based on the detection result, it is possible to obtain the correct distribution of absorption coefficients when collecting transemission CT data, and it is easy to reuse. Since appropriate absorption correction can be performed on the constituent images, a consistent ECT image can be obtained. In addition, since the gamma rays emitted from the surface ray source 10 are focused into a parallel beam by the second parallel hole collimator 11 and the parallel beam is irradiated toward the subject P, the obtained absorption coefficient depends on the subject P. The scattered radiation from the specimen P is also taken into account to some extent, and as a result, the influence of the scattered radiation on the reconstructed image can be reduced at the same time.

Note that when the first detector 5 detects γ-rays emitted from the RI in the subject P, the absorption of γ-rays by the surface ray source 10 is negligibly small (so that the surface ray source 10 It is preferable to make the thickness as thin as possible, and if the second parallel hole collimator 11 has sufficiently higher sensitivity than the first and third parallel hole collimators 9 and 12, it is possible to The difference in sensitivity between the first and second detectors 5.6 for the γ-rays emitted from R1 in P can be made sufficiently small.

Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above-mentioned embodiment, and can be modified as appropriate within the scope of the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to provide an emission CT apparatus that can obtain quantitative ECT images by performing appropriate absorption correction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an emission CT device that is an embodiment of the present invention, FIG. 2 is a block diagram showing details of the arithmetic processing section in the device of this embodiment, and FIG. 3 is a distribution of absorption coefficients in the device of this embodiment. FIG. 4 is a diagram explaining the principle of obtaining projection data in an emission CT apparatus. 5... first detector, 6... second detector, 10.
... Surface radiation source, 21 ... Absorption coefficient calculation means, 23 ...
- Absorption correction means, P...subject. \, -2″

Claims (1)

[Claims] The first and second detectors are equipped with first and second detectors that rotate around the subject while facing each other through the subject and are capable of detecting gamma rays emitted from a radioactive isotope administered to the subject. In an emission CT apparatus that obtains a tomographic image of a subject based on gamma ray information collected by first and second detectors, the first A surface radiation source attached to the front of the detector,
absorption coefficient calculation means for calculating an absorption coefficient of γ-rays based on the γ-rays from the surface ray source detected by the first and second detectors; and absorption coefficient calculation means calculated by the absorption coefficient calculation means. An emission CT apparatus comprising: absorption correction means for performing absorption correction of the tomographic image of the subject using coefficients.